4.12: Student Responses

The following is a summary of the questions in this lab for ease in submitting answers online.

1. Brazil (Latitude and Longitude)

2. Angola (Latitude and Longitude)

3. Measure in centimeters the distance (Map Length) between the two points you recorded in the previous question. Given that this portion of Pangaea broke apart 200,000,000 years ago, calculate how fast South America and Africa are separating in cm/year? (Hint: Speed=DistanceTimeSpeed=DistanceTime)

4. When will the next supercontinent form? Examine the Western Coast of South America, the Eastern Coast of Asia, and the Pacific Ocean. If South America and Africa are separating and the Atlantic Ocean is growing, then the opposite must be occurring on the other side of the earth (the Americas are getting closer to Asia and the Pacific Ocean is shrinking). How far apart are North America and Mainland Asia in cm? (measure the distance across the Pacific at 40 degrees north latitude- basically measure between Northern California and North Korea)? Take that distance and divide it by the speed you calculated in question 3 to estimate when the next supercontinent will form. Show your work!

5. How far have the snake fossils moved apart since they were originally deposited?

a. 1250 miles b. 1700 miles c. 2150 miles d. 2700 miles

6. Given that this portion of the Australian plate moves at a speed of 2.2 inches per year, how old are the snake fossils?

a. 310 million years old b. 217 million years old c. 98 million years old d. 62 million years old e. 34 million years old

7. There are fossils such as Glossopteris and Lystrosaurus that are found in rocks in South America and Africa that indicate they were part of Pangaea approximately 200 million years ago. These same fossils can be found in Australia, which indicates it, along with Antarctica, was also part of Pangaea at that time. Based on your answer to question 6 which of the following statements about the break-up of Pangaea is TRUE?

a. Australia and Antarctica separated before the break-up of Pangaea.

b. Australia and Antarctica separated during the break-up of Pangaea.

c. Australia and Antarctica separated after the break-up of Pangaea.

8. Consider the ages and positions of the islands listed above along with what you know about plate tectonics and hotspots. In what general direction is the Pacific Plate moving?

a. Northwest b. Southeast c. Northeast d. Southwest

9. How fast was the Pacific plate moving during the last 1.1 million years between the formation of the Big Island and Maui in cm/year? To calculate this divide the distance (in centimeters) between the two islands by the difference in their ages.

10. How fast was the Pacific plate moving from 7.2 million years ago to 4.7 million years ago between the formation of Kauai and Nihoa in cm/year? To calculate this divide the distance (in centimeters) between the two islands by the difference in their ages.

11. Examine the headings of the measurements that you took for the previous two questions. The headings indicate the direction the Pacific Plate is moving over the hot spot. How does the direction of motion of the Pacific Plate during the last 1.1 million years differ from the direction of movement between 4.7 and 7.2 million years ago? The direction of plate movement in the last 1.1 million years________.

a. shows no change b. has become more southerly c. has become more northerly

12. Zoom out and examine the dozens of sunken volcanoes out past Nihoa, named the Emperor Seamounts. As one of these volcanic islands on the Pacific Plate moves off the hotspot it becomes inactive, or extinct, and the island begins to sink as it and the surrounding tectonic plates cool down. The speed the islands are sinking can be estimated by measuring the difference in elevation between two islands and dividing by the difference in their ages (this method assumes the islands were a similar size when they were active). Calculate how fast the Hawaiian Islands are sinking, by using the ages and elevations of Maui and Nihoa.

13. Using the speed you calculated in the previous question (and ignoring possible changes in sea level), when will the Big Island of Hawaii sink below the surface of the ocean? Divide the current maximum elevation of the Big Island by the rate you calculated in the previous question.

14. Now zoom out to ~4000 miles eye altitude and look at the chain of Hawaiian Islands again. Notice the chain continues for thousands of miles up to Aleutian Islands (between Alaska and Siberia). Examine the northernmost sunken volcano (50 49 16.99N 167 16 36.12E) in this chain. Where was that volcano located when it was still active, erupting, and above the surface of the ocean?

a. 50 49 16.99N 167 16 36.12E b. 52 31 48.72N 166 25 43.14W

c. 27 45 49.27N 177 10 08.75W d. 19 28 15.23N 155 19 14.43W

15. The rock that most closely resembles the composition of continental crust based on the description in the previous section is:

a. A b. B c. C d. D

16. Based on the choice you made for question 15, what is the density of the rocks that make up continental crust? Please give your answer in grams/milliliter.

17. The rock that most closely resembles the composition of oceanic crust based on the description in the previous section is:

a. A b. B c. C d. D

18. Based on the choice you made for question 17, what is the density of the rocks that make up oceanic crust? Please give your answer in grams/milliliter.

19. Remember, because of isostasy the denser plate will be lower than the less dense plate. If oceanic and continental crust collided, based on their densities the __________ crust would sink below the ________crust.

a. continental; oceanic b. oceanic; continental

20. According to the geothermal gradient, rocks buried 75 km beneath the surface would normally be at what temperature? At 75 km depth, rocks will be heated to about _______ degrees Celsius.

a. 1500 b. 1250 c. 1000 d. 750

21. According to the geothermal gradient, rocks at 500 degrees Celsius will be buried how deep? At 500 degrees Celsius, rocks will be buried to about _______ km depth.

a. 8 b. 12.5 c. 20 d. 27

22. What is the physical state of the dry mantle rock at point X?

a. Completely melted b. Starting to melt c. Completely solid

23. What happens when the lithosphere at point X is heated to 1500 °C?

a. No change b. Starts to crystallize c. Starts to melt

24. At what depth will the dry mantle rock at point X begin to melt if it is uplifted closer to Earth’s surface and its temperature remains the same?

a. 35 km b. 25 km c. 18 km d. 12 km

25. What would happen to the mantle rock at point X if water is added to it?

a. No change b. Starts to crystallize c. Starts to melt

6. Which of the following places represent a Wadati-Benioff zone?

a. 10°S, 110°W b. 0°, 0° c. 15°S, 180° d. 30°N, 75°E

27. The Wadati-Benioff zone is associated with which type of plate boundary?

Type 34 46 16.16 N 118 44 58.19 W into the search bar in Google Earth and zoom out to an eye altitude of 10 miles. Quail Lake is a dammed river that is sitting directly over top of the San Andres Fault, which is a well-known transform boundary with the North American Plate on the northern side and the Pacific Plate on the southern side. This boundary is running East-West in this area and you may be able to see the boundary better by zooming out.

28. Examine the path of the river that feeds into and flows out of Quail Lake. What direction is the North American plate moving in comparison to the Pacific Plate at this location?

a. East b. West

29. Given that San Francisco is located on the North American Plate and Los Angles is located on the Pacific Plate, are these two cities getting closer together or farther apart over time?

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